My grandma who lived through WW2 told me about chicory coffee
Chicory is probably the best known coffee sustitute there is. Been drank in the south since the south has been the south. Very popular in Europe. Was a big hit during the Civil War, too. Mixed half and half with dried and roasted turnips, you get a sweetened "coffee" without using sugar, too.
Dried and roasted grape seed makes for a great coffee sub drinkable; as well as roasted beets (said by some to be actually better than real coffee); dried/roasted acorns from the white oak make a great drink. Only white oak, though, the rest are very bitter with tannin, though some say it's like a good dark roast bitter; half and half coffee and roasted cornmeal (VERY good drink!) or twice the corn if you add no coffee; roasted rye, ground and boiled (roasted and boiled rye is good for peptic ulcers and other stomach probs, too); parsnips, sliced or diced and roasted; well roasted dried split peas make a good drink, anyone can try this one pretty easily; dried and roasted okra seeds (never tried this one but several have said it's great).
The best chicory is dug when the root's driest with little sap ie the late fall and early winter....though few can point out chicory without the flowers. So, when you spot the chicory flowers, mark the stems with a small ribbon and go and dig them later.
God bless.
rich